Terapia antibiótica apropiada en pacientes con Infecciones por Gram negativos: revisión sistemática de la literatura y metaanálisis

1. RESEARCH ARTICLE Open Access
Appropriate initial antibiotic therapy in
hospitalized patients with gram-negative
infections: systematic review and
meta-analysis
Gowri Raman1,2*†
, Esther Avendano1†
, Samantha Berger3
and Vandana Menon2,4
Abstract
Background: The rapid global spread of multi-resistant bacteria and loss of antibiotic effectiveness increases the risk of
initial inappropriate antibiotic therapy (IAT) and poses a serious threat to patient safety. We conducted a systematic
review and meta-analysis of published studies to summarize the effect of appropriate antibiotic therapy (AAT) or IAT
against gram-negative bacterial infections in the hospital setting.
Methods: MEDLINE, EMBASE, and Cochrane CENTRAL databases were searched until May 2014 to identify
English-language studies examining use of AAT or IAT in hospitalized patients with Gram-negative pathogens.
Outcomes of interest included mortality, clinical cure, cost, and length of stay. Citations and eligible full-text articles
were screened in duplicate. Random effect models meta-analysis was used.
Results: Fifty-seven studies in 60 publications were eligible. AAT was associated with lower risk of mortality (unadjusted
summary odds ratio [OR] 0.38, 95 % confidence interval [CI] 0.30-0.47, 39 studies, 5809 patients) and treatment failure (OR
0.22, 95 % CI 0.14–0.35; 3 studies, 283 patients). Conversely, IAT increased risk of mortality (unadjusted summary OR 2.66,
95 % CI 2.12–3.35; 39 studies, 5809 patients). In meta-analyses of adjusted data, AAT was associated with lower
risk of mortality (adjusted summary OR 0.43, 95 % CI 0.23–0.83; 6 studies, 1409 patients). Conversely, IAT increased
risk of mortality (adjusted summary OR 3.30, 95 % CI 2.42–4.49; 16 studies, 2493 patients). A limited number of
studies suggested higher cost and longer hospital stay with IAT. There was considerable heterogeneity in the
definition of AAT or IAT, pathogens studied, and outcomes assessed.
Discussion: Using a large set of studies we found that IAT is associated with a number of serious
consequences,including an increased risk of hospital mortality. Infections caused by drug-resistant, Gram-negative
organisms represent a considerable financial burden to healthcare systems due to the increased costs associated
with the resources required to manage the infection, particularly longer hospital stays. However, there were
insufficient data that evaluated AAT for the outcome of costs among patients with nosocomialGram-negative
infections.
(Continued on next page)
* Correspondence: graman@tuftsmedicalcenter.org
†
Equal contributors
1
Center for Clinical Evidence Synthesis, Institute for Clinical Research and
Health Policy Studies, Tufts Medical Center, Box 63, 800 Washington Street,
Boston, MA 02111, USA
2
Tufts University School of Medicine, 145 Harrison Avenue, Boston, MA
02111, USA
Full list of author information is available at the end of the article
© 2015 Raman et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Raman et al. BMC Infectious Diseases (2015) 15:395
DOI 10.1186/s12879-015-1123-5

2. (Continued from previous page)
Conclusions: IAT in hospitalized patients with Gram-negative infections is associated with adverse outcomes.
Technological advances for rapid diagnostics to facilitate AAT along with antimicrobial stewardship, surveillance,
infection control, and prevention is needed.
Keywords: Appropriate initial antibiotic therapy, Inappropriate initial antibiotic therapy, Hospital-acquired,
Healthcare-associated, Gram-negative, Systematic review
Background
In 2011, there were approximately two million cases
of hospital-acquired infections in the United States,
more than 75,000 of which were fatal [1]. Gram-
negative bacteria cause the four most frequent types
of hospital-acquired infection: pneumonia, intra-
abdominal infection, urinary tract infection (UTI),
and bloodstream infection. In the US from 2009 to
2010, 43 % of healthcare-associated infections, 65 %
of catheter-associated UTIs, 65 % of pneumonia, and
22 % of central line-associated bloodstream infections
were attributed to Gram-negative pathogens [2]. The
most important Gram-negative pathogens in the hospital
setting include Escherichia coli, Klebsiella pneumoniae,
and Pseudomonas aeruginosa, which account for 27 %
of all pathogens and 70 % of all Gram-negative patho-
gens causing healthcare-associated infections [2]. Gram-
negative bacteria develop resistance to commonly pre-
scribed antibiotics through mutation and gene acquisition.
The incidence of multidrug-resistant, Gram-negative
pathogens is on the rise and these organisms represent
an urgent threat due to the limited availability of viable
therapeutic options [3, 4]
Antibiotic treatment guidelines consistently recom-
mended empiric therapy upon patient presentation with
symptoms suggestive of bacterial infection. The potential
for resistance must be considered when selecting empiric/
initial antibiotic therapy because failure to cover the infec-
tious pathogen (s) is associated with negative outcomes
among patients with critical conditions [3]. Although it
is well-known that appropriate initial antibiotic therapy
(AAT) is associated with favorable outcomes among
patients with Gram-negative bacteria, there is a need for
an in-depth, comparative analysis of the contemporary
literature reporting on outcomes associated with AAT
or inappropriate initial antibiotic therapy (IAT). While
a number of recent systematic reviews examined the
role of resistant pathogens on mortality, as compared
with susceptible pathogens, in general, there is a scar-
city of information on the role of the timeliness and
appropriateness of initial antibiotic therapy in these re-
views [5, 6]. In addition, there is considerable lack of infor-
mation if the effect of AAT as compared with IAT in
gram-negative bacterial infections varied by the type of in-
fecting pathogen.
Methods
We conducted a systematic review and meta-analysis of
existing studies on the effectiveness of AAT and IAT for
Gram-negative bacterial infections in the hospital setting
on clinical and economic outcomes, including cost,
length of hospital stay, mortality, and bacterial eradication.
This review was conducted according to the Preferred
Reporting Items for Systematic Reviews and Meta-Analyses
(PRISMA) Statement [7].
Data sources and study selection
Initial comprehensive literature searches were conducted
in MEDLINE, Cochrane CENTRAL, and EMBASE data-
bases from inception through May 2014 for English-
language articles published on the use of appropriate or
inappropriate empiric/initial antibiotics in patients with
hospital-acquired or healthcare-associated Gram-negative
bacteria. The searches combined terms for Gram-negative
bacteria, appropriate or inappropriate initial antimicrobial
therapy, nosocomial or hospital-acquired or healthcare-
associated bacterial acquisition, and infections of desired
sites such as UTI, intra-abdominal infections, bloodstream
infection, and pneumonia. Additional studies were identi-
fied by perusing reference lists of systematic reviews and
economic reviews or obtained from experts. The results of
the literature searches were screened in duplicate using
study eligibility criteria; discrepancies were resolved by
consensus in group conference. Most publications identi-
fied by our initial search examined the effect of use of
AAT or IAT on mortality. Therefore, searches were
expanded to include community-acquired Gram-negative
infections to identify additional articles relevant to eco-
nomic outcomes of length of stay or cost.
Study inclusion criteria
We included studies of adult patients with susceptible,
resistant, or multidrug-resistant Gram-negative infec-
tions of the following sites: respiratory, intra-abdominal,
bloodstream, and urinary tract. While studies with noso-
comial, hospital-acquired, or healthcare-associated infec-
tions were included for all outcomes, studies with
community-acquired Gram-negative infections were in-
cluded only for the outcomes of length of stay and cost.
Patients had to have been given empiric antibiotic therapy
prior to the identification of culture results. Individual
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 2 of 11

3. study definitions of AAT or IAT were accepted. Add-
itional study inclusion criteria included sample size of at
least 10 patients per comparison group (AAT versus IAT)
evaluating at least one of the following outcomes: mortal-
ity, clinical success, microbiologic eradication, length of
stay (hospital and intensive care unit [ICU]), or cost. For
studies with multiple publications on the same Gram-
negative organism, we included those with the longest
recruitment period or longest follow-up, largest sample
size, or both. Unpublished literature was not included, and
no authors were directly contacted for unpublished data.
Study exclusion criteria
We excluded narrative reviews, cross-sectional studies, case
reports, editorials, letters, comments, and non–English-
language articles. Studies that included patients with
Gram-positive bacteria, fungi, or polymicrobial infection
that did not stratify results by Gram-negative bacteria
were excluded. Studies where all patients (100 %) received
either AAT or IAT were excluded.
Data extraction and quality assessment
Each article was screened by one of three investigators and
confirmed by at least one other. Included studies were then
extracted independently, and results were confirmed by
one of the other investigators. The extracted data included
study design; participant characteristics; comorbidity score;
comorbidities; site of infection; primary cause of infection;
history of antibiotic use; history of hospitalization; inclu-
sion criteria; exclusion criteria; definitions of AAT or IAT;
percentage of patients receiving AAT; percentage of pa-
tients receiving IAT; and unadjusted or adjusted analyses
comparing outcomes of interest in patients who received
AAT or IAT.
Data synthesis and analysis
We considered the following outcomes for inclusion in the
meta-analysis: all-cause mortality in hospital, infection-
related mortality, length of stay, hospital costs (as defined
by study authors as direct and indirect costs incurred dur-
ing an inpatient stay, or as hospital accounting costs), and
clinical cure or microbiological clearance. Meta-analysis
was conducted using the random effects model; results are
reported as summary odds ratio (OR) [8]. The random
effects meta-analyses assessed any potential differential
impact of AAT or IAT on the outcomes of interest using
unadjusted and adjusted data, when feasible. The propor-
tion of IAT and the proportion of AAT add up to 100 % for
unadjusted mortality data and results data were rounded
to two decimal places. Cochran’s Q chi-square test was
used to test for between-study heterogeneity and quanti-
fied with I2
[9]. Additional subgroup analyses were con-
ducted by outcome time points, site of infection, pathogen
and definition of AAT. For meta-analyses with at least 10
studies, we evaluated the potential for publication bias with
funnel plots and Egger’s tests for small study effects [10].
We looked for differences across studies using stratified
analyses to explain heterogeneity in association results. To
assess study quality, we applied quality questions from the
Newcastle–Ottawa Quality Assessment Scale for case-
control and observational studies [11]. When feasible, sen-
sitivity analyses were conducted by excluding studies that
were rated as having high risk of bias. All analyses were
performed in Stata version 13 (StataCorp, College Station,
Texas).
This review evaluated data from published studies and
was exempt from ethics committee approval. This review
did not involve any direct research on patients, and no
informed consent was required.
Results
The literature search identified a total of 2391 abstracts,
of which we screened 294 in full text and added seven
articles from existing systematic reviews and by experts.
A total of 57 studies in 60 publications were included
(Fig. 1). In addition, the figure includes the reasons why
the 241 full-text articles were excluded.
Appropriate use of antibiotic therapy was defined het-
erogeneously among 68 % of included studies using both
susceptibility and timeliness. About 20 % of studies
reported susceptibility to at least one empiric antibiotic
therapy by subsequent culture examination as the defin-
ition of AAT. The administration of empiric antibiotics
within a specified number of hours of index infection
site culture was reported as the only definition in 8 % of
studies. The specified number of hours varied between
24 and 72 h. There were no definitions reported for
AAT in 4 % of studies.
Only one-half of the eligible studies adjusted for con-
founders in their analyses for outcomes of interest.
Seven studies (12 %) included only resistant pathogens
and the remaining studies included both resistant and
susceptible pathogens. Patients with resistant pathogens
differed in sex distribution, associated co-morbid condi-
tions, had central venous catheter or urinary catheter, or
had an ICU stay, as compared with those with suscep-
tible pathogens.
Of the five outcomes examined, mortality was the only
endpoint for which a meta-analysis was feasible. For the
other four outcomes, a meta-analysis was not possible
due to insufficient data or heterogeneity of data. For the
mortality analysis, we were able to stratify by reported
outcome time point, the type of pathogen, definition of
AAT, and ICU-related infection.
Mortality outcomes
Thirty-nine studies in 41 publications representing a
total of 5809 patients examined the outcome of mortality
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 3 of 11

4. [12–53] (see Additional file 1: Table S1). Of these, five
were prospective observational studies and 34 were retro-
spective (see Additional file 2: Table S2). Most retrospect-
ive studies identified eligible patients from hospital
administration databases, and four studies examined pa-
tients admitted to the ICU [12, 18, 27, 48]. All studies
were conducted in academic hospitals or tertiary care cen-
ters and most were single-center studies, except for two
multicenter studies [42, 47].
Included studies were conducted in the US (five studies),
Europe (17 studies), Asia (14 studies), and South America
(three studies). The average age of patients among included
studies ranged between 41 and 76 years. The proportion of
men included in studies ranged from 49 to 81 %. The ma-
jority of infections examined were bloodstream infections;
only five studies evaluated patients with hospital-acquired
pneumonia. Mortality was reported within 14 days (12
studies) and 30 days (22 studies) with two studies reporting
at both time points [19, 43]; the mortality time point was
not documented in seven studies. Only four studies re-
ported data on infection-related mortality [14, 22, 24, 53].
Twenty-nine studies (72.5 %) reported any baseline
comorbidity score, heterogeneously, with higher base-
line scores among non-survivors (see Additional file 1:
Table S1). Coexisting conditions among included study
populations were diabetes (0.6 to 40 %), immunosup-
pression (3.5 to 100 %), kidney disease (4 to 37.6 %),
cardiovascular diseases (5 to 81 %), cerebrovascular dis-
eases (0.8 to 50 %), chronic obstructive pulmonary diseases
(7.9 to 31 %), cancers (7.5 to 100 %), hypertension (22.1 to
52.6 %), artery disease (10 to 17.2 %), liver disease/cirrhosis
(1.9 to 15.4 %), and lung disease/dysfunction (9 to 17.4 %).
All 39 studies reported unadjusted data on the associ-
ation of AAT and mortality. The meta-analysis of un-
adjusted data demonstrated a statistically significant
decreased mortality in those who received AAT com-
pared to those who received IAT (39 studies, 5809 pa-
tients, unadjusted summary OR 0.38, 95 % CI 0.30–0.47;
I2
= 64.9 %). Stratified analyses by mortality time point
concurred with the overall unadjusted mortality (Figs. 2,
3 and 4). Additional stratified meta-analyses of studies
that defined the use of AAT by timeliness of index
Fig. 1 PRISMA flow diagram
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 4 of 11

5. culture and studies that examined extended-spectrum β-
lactamase E. coli and Klebsiella spp were homogeneous
(Table 1). Conversely, IAT increased risk of mortality
(unadjusted summary OR 2.66, 95 % CI 2.12–3.35; 39
studies, 5809 patients).
Twenty-two of 39 studies reported data for an
adjusted meta-analysis (Fig. 5). Adjusted data from
16 studies (2493 patients) demonstrated increased
mortality with IAT (adjusted summary OR 3.30, 95 % CI
2.42–4.49, I2
54 %) or decreased mortality in 6 studies
Fig. 3 Whisker plot of unadjusted mortality at 14 days among patients receiving AAT
Fig. 2 Whisker plot of unadjusted mortality at 30 days among patients receiving AAT
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 5 of 11

6. (1409 patients) with AAT (adjusted summary OR 0.43,
95 % CI 0.23–0.83, I2
75 %).
Funnel plots of all studies reporting unadjusted and
adjusted mortality with IAT indicated no potential for
missing studies with inverse associations (RR <1.0).
Economic outcomes
Seventeen studies in 19 publications representing a total
of 3855 patients examined the economic outcomes of
cost or length of stay [17, 22, 25, 31, 38, 46, 54–66].
None were prospective, and all 17 were retrospective
observational studies (see Additional file 3 Tables S3
and S4). Included studies were conducted in the US (six
studies), Europe (four studies), Asia (six studies), and
Israel (one study). The majority of infection was blood-
stream infections (10 studies), and the remainder were
UTIs (three studies), pneumonia (two studies), and intra-
abdominal infections (two studies).
Of the 10 studies that examined cost outcomes, four
provided direct evidence of an association between IAT
and cost, the remaining six provided indirect evidence for
an association. In four studies with the direct evidence of
an association between IAT and cost, IAT was associated
with higher mean total cost (two studies), hospital costs
(two studies), or antibiotic cost (one study). In six studies
with indirect evidence, patients with resistant organisms
received more IAT than those with susceptible organisms,
and the resistant groups had higher mean total cost (two
studies), hospital costs (two studies), antibiotic cost (one
study), or per-patient cost (one study) compared with the
susceptible group.
Heterogeneity of outcomes precluded a meta-analysis
and only a small number of studies reported quantitative
data for direct evidence. IAT was associated with longer
hospital stay (five studies), but shorter ICU stay (two
studies). Receiving IAT was associated with higher hospital
cost (two studies; median = $51,977; interquartile range
[IQR] $34,644–$69,311) and longer hospital stay (five
studies; median = 21; IQR 13–21 days) as compared
with AAT (median = $40,187; IQR $25,982–$54,392;
median = 18; IQR 9–24 days, respectively).
Clinical response outcomes
Five studies reported data on clinical response including
microbiological clearance (one study) and treatment fail-
ure (four studies) [17, 67–70]. The lone study on micro-
biological clearance identified that IAT was significantly
associated with a slower initial rate of bacterial clear-
ance, as compared with AAT [67]. All four studies in un-
adjusted analyses and one study in adjusted analysis
found statistically significant decreased treatment failure
with AAT, as compared with IAT [17, 68–70]. The
meta-analysis of unadjusted data demonstrated a statisti-
cally significant decreased treatment failure with AAT
(three studies, 283 patients, OR 0.22, 95 % CI 0.14–
0.35), as compared with IAT. Only one study that mea-
sured treatment failure defined as persistence of the
presenting signs of infection 72 h after initial culture
collection [68].
Discussion
This systematic review of the literature demonstrates the
impact of the use of AAT or IAT on clinical and economic
outcomes among patients hospitalized with Gram-negative
infections. A meta-analysis of studies examining the impact
of use of AAT in hospital-acquired, Gram-negative infec-
tion indicates a significant decrease in risk for mortality
compared with the use of IAT. Hospital and ICU length of
Fig. 4 Whisker plot of unadjusted in-hospital mortality among patients receiving AAT
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 6 of 11

7. stay was prolonged with IAT compared with AAT. There
were insufficient data that evaluated AAT for the outcome
of costs among patients with nosocomial infections.
The discovery and development of antibiotics is one of
the major health advances of the 20th century; however,
the global spread of antimicrobial resistance is rendering
many commonly-used antibiotics obsolete [71]. The
development of resistance occurs naturally over time,
but is accelerated through the overuse and/or misuse of
antibacterial therapies [72–74]. The rapid global spread
of resistant bacteria and subsequent loss of antibiotic
effectiveness increases the risk of IAT in two ways: first,
patients with resistant infections may initially be given a
drug with little or no activity due to resistance,
effectively delaying the time to treating the pathogen
and, second, the need to treat resistant infections may
lead to antibiotics with proven activity being used too
widely and too early, further promoting the spread of re-
sistance and perpetuating the cycle. Guidelines recom-
mend empiric therapy coverage against anticipated
pathogen and resistance that should be started upon pa-
tient presentation with symptoms suggestive of bacterial
infection. This should be followed by de-escalation ther-
apy once the pathogen and sensitivities are known.
IAT is associated with a number of serious conse-
quences, including an increased risk of hospital mortality.
A US single-center, retrospective cohort study assessing
the role of multidrug resistance in patients with Gram-
Table 1 Subgroup analyses of unadjusted mortality in hospitalized patients receiving AAT
Characteristics Subgroups N Studies Unadjusted OR Results: 95 % CI I2
Cochran Q
p-value
Main analysis All patients 39 0.38 0.30, 0.47 64.9 % <0.001
Non-Acinetobacter Excluding Acinetobacter spp studies 24 0.46 0.34, 0.60 61.4 % <0.001
Mortality outcome time point 14-day 12 0.40 0.29, 0.55 44 % 0.05
30-day 21 0.35 0.25, 0.48 68.5 % <0.001
In-hospital (time NR) 8 0.51 0.30, 0.85 70.6 % 0.001
Pathogen Acinetobacter 15 0.29 0.21, 0.39 51.9 % 0.01
Gram-negative 6 0.27 0.13, 0.53 81.1 % <0.001
ESBL E. coli 4 0.66 0.35, 1.22 18.7 % 0.30
Klebsiella 3 1.00 0.57, 1.78 16.6 % 0.30
pseudomonas 11 0.41 0.29, 0.60 45.0 % 0.05
Pathogen and source of infection ESBL BSI 6 0.71 0.38, 1.31 48.1 % 0.086
Klebsiella BSI 2 0.74 0.37, 1.46 0.0 % 0.453
A Pneumonia 2 0.24 0.14, 0.40 0.0 % 0.466
A BSI 13 0.30 0.21, 0.43 57.4 % 0.005
P. pneumonia 2 0.58 0.18, 1.89 77.4 % 0.036
P BSI 9 0.38 0.26, 0.56 35.6 % 0.133
Gram-negative BSI 4 0.33 0.16, 0.70 83.7 % <.0001
Gram-negative pneumonia 1 0.09 0.03, 0.30 NA NA
ICU-related infections by included subjects ≤50% 12 0.413 0.30, 0.57 40.5 % <0.001
>50% 23 0.38 0.27, 0.53 68.9 % 0.07
Not reported 4 0.27 0.11, 0.67 83.2 % <0.001
AAT timeliness with regard to initial culture ≤24 h 11 0.50 0.35, 0.71 50.1 % 0.024
≤48 h 9 0.40 0.22, 0.72 78.8 % <0.001
≤72 h 7 0.29 0.22, 0.39 0.0 % 0.73
Timeliness NR 10 0.32 0.20, 0.52 66.2 % 0.001
Definitions of AAT Timeliness and susceptibility 26 0.37 0.28, 0.49 68.3 % <0.001
Timeliness alone 3 0.56 0.25, 1.23 35.4 % 0.213
Susceptibility alone 8 0.36 0.23, 0.55 50.0 % 0.051
Not reported 2 0.31 0.03, 3.61 90.1 % 0.001
A Acinetobacter, AAT Appropriate initial antibacterial therapy, BSI Blood stream infection, CI Confidence Interval, E.coli Escherichia coli, ESBL Extended spectrum
beta-lactamase, hr hour, ICU Intensive care unit, OR Odds ratio, P Pseudomonas, N Number, NR Not reported
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 7 of 11

8. negative sepsis and septic shock found that a higher pro-
portion of patients who had a multidrug-resistant infection
or received IAT died [75]. Non-survivors were three times
more likely to receive IAT than those patients who sur-
vived their hospitalization (43.4 % vs. 14.6 %) highlighting
the fact that IAT is a key predictor of mortality in patients
with serious Gram-negative infections [75].
Infections caused by drug-resistant, Gram-negative
organisms represent a considerable financial burden to
healthcare systems due to the increased costs associ-
ated with the resources required to manage the infec-
tion, particularly longer hospital stays. In 2009, the
European Centre for Disease Prevention and Control
and the European Medicines Agency estimated that the
total healthcare cost incurred in Europe due to resistant
infections totaled at least €1.5 billion each year, with
the main portion accounted for by resistant Gram-
negative pathogens at €867 million. These costs include
additional in-hospital and outpatient care costs and the
societal costs of productivity losses due to absence from
work and death [76]. For the US, estimates are as high
as US$20 billion in extra direct healthcare costs, with
additional costs to society for lost productivity as high
as US$35 billion per year [77].
This review and meta-analysis results should be inter-
preted in light of its limitations. Our inclusion criteria
required that studies only consider hospital-acquired or
healthcare-associated infection and were published in
English for the outcome of mortality. For the evaluation
of economic outcomes, we expanded the eligibility to
community-acquired infection given the paucity of data
on economic outcomes. In addition, the limitations of
this review reflect, to a large extent, the limitations of
the data available in primary studies. There was a gen-
eral lack of adequate accounting for possible con-
founders, with little over one-half of the studies (59 %)
reporting adjusted analyses for mortality outcomes. Con-
founding factors may have influenced the outcome of
mortality in unadjusted analyses. Although the propor-
tion of IAT and the proportion of AAT add up to 100 %
for unadjusted mortality data, both data are presented
for ease of comparison. In contrast, all studies did not
report adjusted data for both groups. Finally, the litera-
ture is heterogeneous with respect to the definition of
use of IAT. As a result, we performed subgroup analyses
based on different definitions reported in studies. Given
the nature of reporting and data collection for the stud-
ies included in this meta-analysis, we were unable to
Fig. 5 Whisker plot of adjusted mortality among patients receiving AAT or IAT
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 8 of 11

9. examine culture negative cases or other definitions of
appropriate therapy such as guideline-concordant. There
were fewer studies that evaluated the outcome of costs
or length of stay for nosocomial infections. These data
are likely an underestimate of the true economic impact
of IAT as they do not account for reduced resource
utilization and shorter hospital stay attributable to the
higher mortality in patients receiving IAT. Analyzing the
impact of resistance on length of stay and costs is diffi-
cult due to competing events of mortality and discharge
or time-dependent bias, which were not appropriately
addressed in most of the included studies.
Conclusions
Resistance rates are increasing among Gram-negative
pathogens that are responsible for serious nosocomial
infections, including P. aeruginosa and extended spectrum
β-lactamase–producing Enterobacteriaceae. Our study pre-
sents a review of contemporaneous literature and demon-
strates that IAT is associated with increased mortality and
prolonged hospital stays that could translate into higher
health care costs. Conversely, AAT improves patient out-
comes and could potentially lead to cost savings. These
findings underscore the need for technological advances
for rapid diagnostics as well as the “treat the right
patient with the right drug at the right time” approach
to treating serious nosocomial infections, particularly
when there is a high clinical suspicion of resistance. A
global multidisciplinary effort to combat resistance that
includes antimicrobial stewardship, infection control and
prevention, and the development of new antimicrobial
agents with activity against multidrug-resistant Gram-
negative pathogens is critical to combat this public health
threat and prolong the effectiveness of existing antibiotics.
Additional files
Additional file 1: Table S1. Characteristics of included studies reporting
mortality outcomes. (DOCX 98 kb)
Additional file 2: Table S2. Additional characteristics of included studies
reporting mortality outcomes. (DOCX 95 kb)
Additional file 3: Table S3. Study characteristics and results of economic
outcomes. Table S4. Study characteristics and results of length of stay
(DOCX 74 kb)
Abbreviations
AAT: Appropriate antibiotic therapy; CI: Confidence interval; IAT: Inappropriate
antibiotic therapy; ICU: Intensive care unit; IQR: Interquartile range; OR: Odds ratio;
PRISMA: Preferred reporting items for systematic reviews and meta-analyses;
UTI: Urinary tract infection.
Competing interests
GR was a paid consultant to Cubist Pharmaceuticals on a previous project
on “Clinical and economic consequences of hospital-acquired resistant and
multidrug-resistant pseudomonas aeruginosa infections.” EA and SB do not
have any conflicts of interest. VM was an employee of Cubist
Pharmaceuticals.
Authors’ contributions
GR performed the searches, data verification, synthesized and analyzed the
data, and drafted first sections of the text. VM designed the study and
participated in manuscript revisions. EA and SB performed data extraction
and verification, synthesis, and assisted in manuscript preparation. GR, EA,
and SB had full access to all of the data (including extracted data and
statistical reports) in the study and can take responsibility for the integrity
of the data and the accuracy of the data analysis. All authors read and
approved the final manuscript.
Authors’ information
Not applicable.
Availability of data and materials
Not applicable.
Acknowledgments
Some data were previously presented as a poster at the ISPOR 17th Annual
European Congress, Amsterdam, The Netherlands.
Funding
Funding for the completion of the systematic literature review and meta-analysis
was provided by Cubist Pharmaceuticals to the Tufts Medical Center. GR was the
Principal Investigator.
Author details
1
Center for Clinical Evidence Synthesis, Institute for Clinical Research and
Health Policy Studies, Tufts Medical Center, Box 63, 800 Washington Street,
Boston, MA 02111, USA. 2
Tufts University School of Medicine, 145 Harrison
Avenue, Boston, MA 02111, USA. 3
Tufts University Friedman School of
Nutrition Science and Policy, 150 Harrison Avenue, Boston, MA 02111, USA.
4
Currently employed at Baxalta and a former employee of Cubist
Pharmaceuticals, 65 Hayden Avenue, Lexington, MA 02421, USA.
Received: 20 February 2015 Accepted: 14 September 2015
References
1. Healthcare-associated Infections (HAIs). HAI Prevalence Data and Statistics.
Centers for Disease Control and Prevention website. Available online:
http://www.cdc.gov/HAI/surveillance/index.html. Accessed January 12, 2015
2. Sievert DM, Ricks P, Edwards JR, Schneider A, Patel J, Srinivasan A, et al.
Antimicrobial-resistant pathogens associated with healthcare-associated
infections: summary of data reported to the national healthcare safety
network at the centers for disease control and prevention, 2009–2010.
Infect Control Hosp Epidemiol. 2013;34:1–14.
3. Boyd N, Nailor MD. Combination antibiotic therapy for empiric and definitive
treatment of gram-negative infections: insights from the society of infectious
diseases pharmacists. Pharmacotherapy. 2011;31:1073–84.
4. Livermore DM, Woodford N. The beta-lactamase threat in Enterobacteriaceae,
pseudomonas and acinetobacter. Trends Microbiol. 2006;14:413–20.
5. Zimlichman E, Henderson D, Tamir O, Franz C, Song P, Yamin CK, et al. Health
care-associated infections: a meta-analysis of costs and financial impact on the
US health care system. JAMA Intern Med. 2013;173:2039–46.
6. Nathwani D, Raman G, Sulham K, Gavaghan M, Menon V. Clinical and
economic consequences of hospital-acquired resistant and multidrug-resistant
Pseudomonas aeruginosa infections: a systematic review and meta-analysis.
Antimicrob Resist Infect Control. 2014;3:32.
7. Moher D, Liberati A, Tetzlaff J, Altman DG. Preferred reporting items for
systematic reviews and meta-analyses: the PRISMA statement. BMJ.
2010;8:336–41.
8. DerSimonian R, Laird N. Meta-analysis in clinical trials. Control Clin Trials.
1986;7:177–88.
9. Huedo-Medina TB, Sanchez-Meca J, Marin-Martinez F, Botella J. Assessing
heterogeneity in meta-analysis: Q statistic or I2 index? Psychol Methods.
2006;11:193–206.
10. Egger M, Davey SG, Schneider M, Minder C. Bias in meta-analysis detected
by a simple, graphical test. BMJ. 1997;315:629–34.
11. Wells G, Shea B, O’Connell D, Peterson J, Welch V, Losos M, Shea B, O’Connell
D, Peterson J, Welch V, Losos M, Tugwell P: The Newcastle-Ottawa Scale (NOS)
for assessing the quality of nonrandomised studies in meta-analyses. http://
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 9 of 11

10. www.ohri.ca/programs/clinical_epidemiology/oxford.asp. Published 2007.
Accessed January 12, 2015
12. Cordery RJ, Roberts CH, Cooper SJ, Bellinghan G, Shetty N. Evaluation of risk
factors for the acquisition of bloodstream infections with extended-spectrum
beta-lactamase-producing Escherichia coli and Klebsiella species in the intensive
care unit; antibiotic management and clinical outcome. J Hosp Infect.
2008;68:108–15.
13. Du B, Long Y, Liu H, Chen D, Liu D, Xu Y, et al. Extended-spectrum
beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae
bloodstream infection: risk factors and clinical outcome. Intensive Care Med.
2002;28:1718–23.
14. de Gouvea EF, Martins IS, Halpern M, Ferreira AL, Basto ST, Goncalves RT,
et al. The influence of carbapenem resistance on mortality in solid organ
transplant recipients with Acinetobacter baumannii infection. BMC Infect
Dis. 2012;12:351.
15. Edis EC, Hatipoglu ON, Tansel O, Sut N. Acinetobacter pneumonia: Is the
outcome different from the pneumonias caused by other agents. Ann
Thoracic Med. 2010;5:92–6.
16. Erbay A, Idil A, Gozel MG, Mumcuoglu I, Balaban N. Impact of early appropriate
antimicrobial therapy on survival in Acinetobacter baumannii bloodstream
infections. Int J Antimicrob Agents. 2009;34:575–9.
17. Falagas ME, Kasiakou SK, Rafailidis PI, Zouglakis G, Morfou P. Comparison of
mortality of patients with Acinetobacter baumannii bacteraemia receiving
appropriate and inappropriate empirical therapy. J Antimicrob Chemother.
2006;57:1251–4.
18. Garnacho-Montero J, Sa-Borges M, Sole-Violan J, Barcenilla F, Escoresca-Ortega A,
Ochoa M, et al. Optimal management therapy for Pseudomonas aeruginosa
ventilator-associated pneumonia: an observational, multicenter study
comparing monotherapy with combination antibiotic therapy. Crit Care Med.
2007;35:1888–95.
19. Gozel M, Erbay A, Bodur H, Eren S, Balaban N. Risk factors for mortality in
patients with nosocomial gram-negative bacteremia. Turkiye Klinikleri J Med
Sci. 2012;32:1641–7.
20. Huang ST, Chiang MC, Kuo SC, Lee YT, Chiang TH, Yang SP, et al. Risk factors
and clinical outcomes of patients with carbapenem-resistant Acinetobacter
baumannii bacteremia. J Microbiol Immunol Infect. 2012;45:356–62.
21. Jamulitrat S, Arunpan P, Phainuphong P. Attributable mortality of imipenem-
resistant nosocomial Acinetobacter baumannii bloodstream infection. J Med
Assoc Thai. 2009;92:413–9.
22. Joung MK, Kwon KT, Kang CI, Cheong HS, Rhee JY, Jung DS, et al. Impact of
inappropriate antimicrobial therapy on outcome in patients with hospital-
acquired pneumonia caused by Acinetobacter baumannii. J Infect. 2010;61:212–8.
23. Kang CI, Kim SH, Park WB, Lee KD, Kim HB, Kim EC, et al. Bloodstream infections
caused by antibiotic-resistant gram-negative bacilli: risk factors for mortality and
impact of inappropriate initial antimicrobial therapy on outcome. Antimicrob
Agents Chemother. 2005;49:760–6.
24. Kim YJ, Kim SI, Hong KW, Kim YR, Park YJ, Kang MW. Risk factors for mortality in
patients with carbapenem-resistant Acinetobacter baumannii bacteremia:
impact of appropriate antimicrobial therapy. J Korean Med Sci. 2012;27:471–5.
25. Kollef KE, Schramm GE, Wills AR, Reichley RM, Micek ST, Kollef MH. Predictors of
30-day mortality and hospital costs in patients with ventilator-associated
pneumonia attributed to potentially antibiotic-resistant gram-negative bacteria.
Chest. 2008;134:281–7.
26. Kuo SC, Lee YT, Yang SP, Chiang MC, Lin YT, Tseng FC, et al. Evaluation of the
effect of appropriate antimicrobial therapy on mortality associated with
Acinetobacter nosocomialis bacteraemia. Clin Microbiol Infect. 2013;19:634–9.
27. Lee HY, Chen CL, Wu SR, Huang CW, Chiu CH. Risk factors and outcome
analysis of acinetobacter baumannii complex bacteremia in critical patients.
Crit Care Med. 2014;42:1081–8.
28. Lin YT, Chiu CH, Chan YJ, Lin ML, Yu KW, Wang FD, et al. Clinical and
microbiological analysis of Elizabethkingia meningoseptica bacteremia in
adult patients in Taiwan. Scand J Infect Dis. 2009;41:628–34.
29. Lin YT, Liu CJ, Fung CP, Tzeng CH. Nosocomial Klebsiella pneumoniae
bacteraemia in adult cancer patients–characteristics of neutropenic and
non-neutropenic patients. Scand J Infect Dis. 2011;43:603–8.
30. Lodise Jr TP, Patel N, Kwa A, Graves J, Furuno JP, Graffunder E, et al. Predictors of
30-day mortality among patients with Pseudomonas aeruginosa bloodstream
infections: impact of delayed appropriate antibiotic selection. Antimicrob
Agents Chemother. 2007;51:3510–5.
31. Lye DC, Earnest A, Ling ML, Lee TE, Yong HC, Fisher DA, et al. The impact of
multidrug resistance in healthcare-associated and nosocomial Gram-
negative bacteraemia on mortality and length of stay: cohort study. Clin
Microbiol Infect. 2012;18:502–8.
32. Mehta A, Kumar V, Kumari I, Nair S, Dinesh K, Singh S. Risk factors for mortality
in Acinetobacter calcoaceticus-baumannii bacteraemia. Asian Pac J Trop
Biomed. 2012;2:S1852–7.
33. Metan G, Zarakolu P, Cakir B, Hascelik G, Uzun O. Clinical outcomes and
therapeutic options of bloodstream infections caused by extended-spectrum
beta-lactamase-producing Escherichia coli. Int J Antimicrob Agents.
2005;26:254–7.
34. Metan G, Sariguzel F, Sumerkan B. Factors influencing survival in patients
with multi-drug-resistant Acinetobacter bacteraemia. Eur J Intern Med.
2009;20:540–4.
35. Metan G, Demiraslan H, Kaynar LG, Zararsiz G, Alp E, Eser B. Factors influencing
the early mortality in haematological malignancy patients with nosocomial Gram
negative bacilli bacteraemia: a retrospective analysis of 154 cases. Braz J Infect Dis.
2013;17:143–9.
36. Micek ST, Lloyd AE, Ritchie DJ, Reichley RM, Fraser VJ, Kollef MH. Pseudomonas
aeruginosa bloodstream infection: importance of appropriate initial antimicrobial
treatment. Antimicrob Agents Chemother. 2005;49:1306–11.
37. Navarro-San FC, Mora-Rillo M, Romero-Gomez MP, Moreno-Ramos F, Rico-Nieto A,
Ruiz-Carrascoso G, et al. Bacteraemia due to OXA-48-carbapenemase-
producing Enterobacteriaceae: a major clinical challenge. Clin Microbiol
Infect. 2013;19:E72–9.
38. Ng E, Earnest A, Lye DC, Ling ML, Ding Y, Hsu LY. The excess financial burden
of multidrug resistance in severe gram-negative infections in Singaporean
hospitals. Ann Acad Med Singap. 2012;41:189–93.
39. Park KH, Shin JH, Lee SY, Kim SH, Jang MO, Kang SJ, et al. The clinical
characteristics, carbapenem resistance, and outcome of Acinetobacter
bacteremia according to genospecies. PLoS ONE [Electronic Resource].
2013;8:e65026.
40. Pena C, Gudiol C, Calatayud L, Tubau F, Dominguez MA, Pujol M, et al.
Infections due to Escherichia coli producing extended-spectrum beta-
lactamase among hospitalised patients: factors influencing mortality. J Hosp
Infect. 2008;68:116–22.
41. Pena C, Gomez-Zorrilla S, Oriol I, Tubau F, Dominguez MA, Pujol M, et al.
Impact of multidrug resistance on Pseudomonas aeruginosa ventilator-
associated pneumonia outcome: predictors of early and crude mortality. Eur
J Clin Microbiol. 2013;32:413–20.
42. Rodriguez-Bano J, Picon E, Gijon P, Hernandez JR, Cisneros JM, Pena C, et al.
Risk factors and prognosis of nosocomial bloodstream infections caused by
extended-spectrum-beta-lactamase-producing Escherichia coli. J Clin
Microbiol. 2010;48:1726–31.
43. Su TY, Ye JJ, Hsu PC, Wu HF, Chia JH, Lee MH. Clinical characteristics and
risk factors for mortality in cefepime-resistant Pseudomonas aeruginosa
bacteremia. J Microbiol Immunol Infect. 2015;48:175–82.
44. Tam VH, Rogers CA, Chang KT, Weston JS, Caeiro JP, Garey KW. Impact of
multidrug-resistant Pseudomonas aeruginosa bacteremia on patient
outcomes. Antimicrob Agents Chemother. 2010;54:3717–22.
45. Thom KA, Shardell MD, Osih RB, Schweizer ML, Furuno JP, Perencevich EN,
et al. Controlling for severity of illness in outcome studies involving infectious
diseases: impact of measurement at different time points. Infect Control Hosp
Epidemiol. 2008;29:1048–53.
46. Thom KA, Schweizer ML, Osih RB, McGregor JC, Furuno JP, Perencevich EN,
et al. Impact of empiric antimicrobial therapy on outcomes in patients with
Escherichia coli and Klebsiella pneumoniae bacteremia: a cohort study. BMC
Infect Dis. 2008;8:116.
47. Tumbarello M, Viale P, Viscoli C, Trecarichi EM, Tumietto F, Marchese A, et al.
Predictors of mortality in bloodstream infections caused by Klebsiella
pneumoniae carbapenemase-producing K. pneumoniae: importance of
combination therapy. Clin Infect Dis. 2012;55:943–50.
48. Tumbarello M, De PG, Trecarichi EM, Spanu T, Antonicelli F, Maviglia R, et al.
Clinical outcomes of Pseudomonas aeruginosa pneumonia in intensive care
unit patients. Intensive Care Med. 2013;39:682–92.
49. Tuon FF, Kruger M, Terreri M, Penteado-Filho SR, Gortz L. Klebsiella ESBL
bacteremia-mortality and risk factors. Braz J Infect Dis. 2011;15:594–8.
50. Tuon FF, Gortz LW, Rocha JL. Risk factors for pan-resistant Pseudomonas
aeruginosa bacteremia and the adequacy of antibiotic therapy. Braz J Infect
Dis. 2012;16:351–6.
51. Vitkauskiene A, Skrodeniene E, Dambrauskiene A, Macas A, Sakalauskas R.
Pseudomonas aeruginosa bacteremia: resistance to antibiotics, risk factors,
and patient mortality. Medicina (Kaunas). 2010;46:490–5.
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 10 of 11

11. 52. Yang YS, Lee YT, Tsai WC, Kuo SC, Sun JR, Yang CH, et al. Comparison between
bacteremia caused by carbapenem resistant Acinetobacter baumannii and
Acinetobacter nosocomialis. BMC Infect Dis. 2013;13:311.
53. Zarkotou O, Pournaras S, Tselioti P, Dragoumanos V, Pitiriga V, Ranellou K,
et al. Predictors of mortality in patients with bloodstream infections caused
by KPC-producing Klebsiella pneumoniae and impact of appropriate
antimicrobial treatment. Clin Microbiol Infect. 2011;17:1798–803.
54. Apisarnthanarak A, Kiratisin P, Mundy LM. Predictors of mortality from
community-onset bloodstream infections due to extended-spectrum
beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae.
Infect Control Hosp Epidemiol. 2008;29:671–4.
55. Bailey AM, Weant KA, Baker SN. Prevalence and risk factor analysis of resistant
Escherichia coli urinary tract infections in the emergency department. Pharm
Pract. 2013;11:96–101.
56. Bare M, Castells X, Garcia A, Riu M, Comas M, Egea MJ. Importance of
appropriateness of empiric antibiotic therapy on clinical outcomes in
intra-abdominal infections. Int J Technol Assess Health Care.
2006;22:242–8.
57. Lautenbach E, Patel JB, Bilker WB, Edelstein PH, Fishman NO. Extended-spectrum
beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae: risk
factors for infection and impact of resistance on outcomes. Clin Infect Dis.
2001;32:1162–71.
58. Lee NY, Lee HC, Ko NY, Chang CM, Shih HI, Wu CJ, et al. Clinical and
economic impact of multidrug resistance in nosocomial Acinetobacter
baumannii bacteremia. Infect Control Hosp Epidemiol. 2007;28:713–9.
59. Lee SS, Kim Y, Chung DR. Impact of discordant empirical therapy on
outcome of community-acquired bacteremic acute pyelonephritis. J Infect.
2011;62:159–64.
60. MacVane SH, Tuttle LO, Nicolau DP. Impact of extended-spectrum beta-
lactamase-producing organisms on clinical and economic outcomes in
patients with urinary tract infection. J Hosp Med (Online). 2014;9:232–8.
61. Osih RB, McGregor JC, Rich SE, Moore AC, Furuno JP, Perencevich EN, et al.
Impact of empiric antibiotic therapy on outcomes in patients with
Pseudomonas aeruginosa bacteremia. Antimicrob Agents Chemother.
2007;51:839–44.
62. Schwaber MJ, Navon-Venezia S, Kaye KS, Ben-Ami R, Schwartz D, Carmeli Y.
Clinical and economic impact of bacteremia with extended- spectrum-beta-
lactamase-producing Enterobacteriaceae. Antimicrob Agents Chemother.
2006;50:1257–62.
63. Shorr AF, Micek ST, Welch EC, Doherty JA, Reichley RM, Kollef MH. Inappropriate
antibiotic therapy in Gram-negative sepsis increases hospital length of stay. Crit
Care Med. 2011;39:46–51.
64. Sturkenboom MC, Goettsch WG, Picelli G, in ‘t Veld B, Yin DD, De Jong RB,
et al. Inappropriate initial treatment of secondary intra-abdominal infections
leads to increased risk of clinical failure and costs. Br J Clin Pharmacol.
2005;60:438–43.
65. Tumbarello M, Spanu T, Di BR, Marchetti M, Ruggeri M, Trecarichi EM, et al.
Costs of bloodstream infections caused by Escherichia coli and influence of
extended-spectrum-beta-lactamase production and inadequate initial
antibiotic therapy. Antimicrob Agents Chemother. 2010;54:4085–91.
66. Yang YS, Ku CH, Lin JC, Shang ST, Chiu CH, Yeh KM, et al. Impact of
Extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella
pneumoniae on the outcome of community-onset bacteremic urinary tract
infections. J Microbiol Immunol Infect. 2010;43:194–9.
67. Chuang YC, Chang SC, Wang WK. Using the rate of bacterial clearance
determined by real-time polymerase chain reaction as a timely surrogate
marker to evaluate the appropriateness of antibiotic usage in critical
patients with Acinetobacter baumannii bacteremia. [Erratum appears in
Crit Care Med. 2012;40(10):2932]. Crit Care Med 2012, 40:2273–2280.
68. O’Neal CS, O’Neal HR, Daniels TL, Talbot TR. Treatment outcomes in patients
with third-generation cephalosporin-resistant Enterobacter bacteremia.
Scandinavian J Infect Dis. 2012;44:726–32.
69. Santimaleeworagun W, Wongpoowarak P, Chayakul P, Pattharachayakul S,
Tansakul P, Garey KW. Clinical outcomes of patients infected with carbapenem-
resistant Acinetobacter baumannii treated with single or combination antibiotic
therapy. J Med Assoc Thai. 2011;94:863–70.
70. Shime N, Kosaka T, Fujita N. De-escalation of antimicrobial therapy for
bacteraemia due to difficult-to-treat Gram-negative bacilli. Infection.
2013;41:203–10.
71. Davies J, Davies D. Origins and evolution of antibiotic resistance. Microbiol
Mol Biol Rev. 2010;74:417–33.
72. Threat Report 2013: Antibiotic/Antimicrobial Resistance. Centers for Disease
Control and Prevention. Available online: http://www.cdc.gov/drugresistance/
threat-report-2013/. Published 2013. Accessed on January 12, 2015
73. Pallett A, Hand K. Complicated urinary tract infections: practical solutions for the
treatment of multiresistant Gram-negative bacteria. J Antimicrob Chemother.
2010;65 Suppl 3:iii25–33.
74. Bader MS, Hawboldt J, Brooks A. Management of complicated urinary tract
infections in the era of antimicrobial resistance. Postgrad Med. 2010;122:7–15.
75. Zilberberg MD, Shorr AF, Micek ST, Vazquez-Guillamet C, Kollef MH. Multi-drug
resistance, inappropriate initial antibiotic therapy and mortality in Gram-negative
severe sepsis and septic shock: a retrospective cohort study. Crit Care.
2014;18:596.
76. The bacterial challenge: time to react. Available online: http://ecdc.europa.eu/
en/publications/Publications/
0909_TER_The_Bacterial_Challenge_Time_to_React.pdf. Published on 2009.
Accessed on January 12, 2015
77. Lautenbach E, Perencevich EN. Addressing the emergence and impact of
multidrug-resistant gram-negative organisms: a critical focus for the next
decade. Infect Control Hosp Epidemiol. 2014;35:333–5.
Submit your next manuscript to BioMed Central
and take full advantage of:
• Convenient online submission
• Thorough peer review
• No space constraints or color figure charges
• Immediate publication on acceptance
• Inclusion in PubMed, CAS, Scopus and Google Scholar
• Research which is freely available for redistribution
Submit your manuscript at
www.biomedcentral.com/submit
Raman et al. BMC Infectious Diseases (2015) 15:395 Page 11 of 11